Communication apparatus and communication method

ABSTRACT

A communication apparatus performs packet transmission at the time of detecting an interference signal. Each STA records a pair of a measurement result of an RSSI of an OBSS and a BSS Color, and reports, to an AP, BSS Colors that correspond to a maximum value and a minimum value of the RSSI. The AP generates a database or a table by using a STA having a minimum or maximum RSSI for each of the OBSS&#39;s. When a signal of an OBSS is detected, the AP selects a STA that has the smallest RSSI of the OBSS or does not have the largest RSSI of the OBSS, and performs SR transmission.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase of International PatentApplication No. PCT/JP2017/039548 filed on Nov. 1, 2017, which claimspriority benefit of Japanese Patent Application No. JP 2016-246456 filedin the Japan Patent Office on Dec. 20, 2016. Each of theabove-referenced applications is hereby incorporated herein by referencein its entirety.

TECHNICAL FIELD

A technology disclosed herein relates to a communication apparatus and acommunication method that are capable of performing transmissionprocessing in a state of detecting an interference signal (such as asignal that arrives from an adjacent cell).

BACKGROUND ART

IEEE 802.11 serving as one example of a representative standard for awireless LAN defines carrier sense multiple access/collision avoidance(CSMA/CA) as a mechanism in which each terminal station autonomouslyacquires a transmission opportunity. Specifically, a terminal stationperforms transmission standby (backoff) during a random time period, andobserves ambient radio wave environment (performs carrier sensing)during this backoff. When the terminal station detects radio waveshaving a power that is greater than or equal to a certain detectionthreshold, the terminal station stops backoff, and suppressestransmission of a packet. Due to this mechanism of backoff and carriersensing, the terminal station avoids packet collision while acquiring atransmission opportunity in an autonomous distributed manner.

However, in an environment in which many terminal stations exist in highdensity, if the detection of radio waves and the avoidance of collisionthat are described above are performed by using a detection thresholdset according to the IEEE 802.11 standard, for example, a signal thathas been transmitted from a terminal station that belongs to an adjacentcell is detected, and transmission is suppressed excessively orunnecessarily. Such a case has been regarded as a problem. Note that the“cell” described above is equivalent to, for example, a basic serviceset (BSS) that a base station configures together with terminal stationsunder control. Furthermore, the adjacent cell is equivalent to anotherBSS having an overlapping receivable range (hereinafter also referred toas an “overlapping basic service set (OBSS)”).

Accordingly, for example, in IEEE 802.11ax serving as one example of anext-generation wireless LAN standard, a spatial reuse (SR) technologyhas been being examined in which adjacent cells reuse a single frequencychannel and frequency resources are efficiently used. Specifically, evenif terminal stations in cells adjacent to each other detect a signalfrom each other, the terminal stations are enabled to transmit their ownpackets. The SR technology described above can be realized by describinga simplified BSS identifier called a “BSS Color” in a PHY header of apacket so as to enable a reception side to discriminate a signal(hereinafter also referred to as a “local-cell signal”) of a BSS (thelocal cell) that the reception side belongs to from a signal(hereinafter also referred to as an “adjacent-cell signal”) from an OBSS(an adjacent cell) on the basis of the BSS Color described in the PHYheader (see, for example, Patent Document 1).

For example, in a case where a terminal station that has received apacket can determine that the packet is an adjacent-cell signal on thebasis of the content described in the PHY header, the terminal stationinterrupts the reception of a packet at this point in time. Moreover, ifthe reception power of the received signal is less than or equal to adetection threshold (an OBSS-power detection (PD) threshold) of theadjacent-cell signal, the start of backoff is permitted. This enablesspatial reuse to be realized. Due to spatial reuse, even if a signal isstill being transmitted from the OBSS, an opportunity to transmit asignal to the terminal station increases. This results in improvementsin a throughput of the entirety of a system.

Note that, in SR transmission based on the detection of the OBSS-PDthreshold, the OBSS-PD threshold is generally adjusted. For example, theterminal station can increase the OBSS-PD threshold by reducing its owntransmission power, and can easily acquire a transmission opportunityusing spatial reuse by adjusting the transmission power according tointerference power.

CITATION LIST Patent Document

-   Patent Document 1: Japanese Patent Application Laid-Open No.    2016-28465

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

It is an object of the technology disclosed herein to provide acommunication apparatus and a communication method having high qualitythat are capable of suitably performing transmission processing in astate of detecting an interference signal.

Solutions to Problems

The technology disclosed herein has been made in consideration of theproblems above. A first aspect of the technology disclosed herein is acommunication apparatus including:

a communication unit that transmits or receives a signal;

an information obtaining unit that obtains information relating tointerference that each transmission destination candidate receives froman interference source; and

a controller that selects each of the transmission destinationcandidates on the basis of the information when an interference signalarrives.

Furthermore, a second aspect of the technology disclosed herein is acommunication method including:

an information obtaining step of obtaining information relating tointerference that each transmission destination candidate receives froman interference source; and

a controlling step of selecting each of the transmission destinationcandidates on the basis of the information when an interference signalarrives.

Furthermore, a third aspect of the technology disclosed herein is acommunication apparatus that operates under a control of an accesspoint, the communication apparatus including:

a controller that performs control to transmit, to the access point,information relating to an intensity of a received signal of an OBSSsignal.

Effects of the Invention

According to the technology disclosed herein, a communication apparatusand a communication method having high quality can be provided that arecapable of suitably performing transmission processing in a state ofdetecting an interference signal.

Note that effects described herein are merely examples, and effects ofthe present invention are not limited to the effects described herein.Furthermore, the present invention further exhibits additional effectsin addition to the effects described above in some cases.

Yet other objects, features, and advantages of the technology disclosedherein will be clarified by a more detailed description based on theembodiments described later and the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of an ideal configuration of a wirelessLAN system to which SR transmission based on OBSS-PD is applied.

FIG. 2 illustrates an example of a signal transmission sequence in awireless LAN system 100 illustrated in FIG. 1.

FIG. 3 illustrates an example of a configuration of a wireless LANsystem 300.

FIG. 4 is a flowchart illustrating a processing procedure performed whena terminal station receives a frame.

FIG. 5 is a block diagram illustrating an example of implementation forrecording reception power and a BSS Color of an OBSS signal.

FIG. 6 is a flowchart illustrating a processing procedure for reportingOBSS RSSI information to an AP.

FIG. 7 illustrates an example of a configuration of a measurement reportframe.

FIG. 8 illustrates an example of a table that reflects a roughpositional relationship among each STA under the control of the AP,OBSS's, and the AP.

FIG. 9 is a diagram explaining an example of a method in which the APrealizes SR transmission based on OBSS-PD.

FIG. 10 illustrates an example of a signal transmission sequence at atime when the AP realizes SR transmission based on OBSS-PD.

FIG. 11 is a diagram explaining another example of the method in whichthe AP realizes SR transmission based on OBSS-PD.

FIG. 12 illustrates an example of a signal transmission sequence at atime when the AP realizes SR transmission based on OBSS-PD.

FIG. 13 is a diagram explaining another example of the method in whichthe AP realizes SR transmission based on OBSS-PD.

FIG. 14 illustrates an example of a signal transmission sequence at atime when the AP realizes SR transmission based on OBSS-PD.

FIG. 15 is a flowchart illustrating a processing procedure in which theAP realizes SR transmission based on OBSS-PD.

FIG. 16 illustrates an example of a configuration of a wireless LANsystem 1600.

FIG. 17 illustrates a result of performing clustering processing on thewireless LAN system 1600 illustrated in FIG. 16.

FIG. 18 illustrates an example of a table obtained by dividing STAs andOBSS's into clusters on the basis of an arrival angle.

FIG. 19 is a flowchart illustrating a processing procedure in which theAP realizes SR transmission based on OBSS-PD.

FIG. 20 illustrates an example of a functional configuration of acommunication apparatus 2000.

MODE FOR CARRYING OUT THE INVENTION

Embodiments of the technology disclosed herein are described below indetail with reference to the drawings.

FIG. 1 schematically illustrates an example of an ideal configuration ofa wireless LAN system 100 to which SR transmission based on OBSS-PD isapplied. The illustrated wireless LAN system 100 includes a plurality ofbase stations (access points: APs) and a plurality of terminal stations(stations: STAs) among which connection has been established. It isassumed that an interference source such as an adjacent cell or anothersystem exists around the wireless LAN system 100. In the illustratedexample, a BSS that an AP configures together with STA 1 to STA 3 undercontrol is denoted by reference number 101. Furthermore, an OBSS (anOBSS-STA) having a receivable range that overlaps a receivable range ofthe BSS 101 is denoted by reference number 102. From among STA 1 to STA3 under the control of the AP, STA 1 and STA 3 have a receivable rangethat overlaps a receivable range of the OBSS 102, but STA 2 does nothave a receivable range that overlaps the receivable range of the OBSS102.

Furthermore, FIG. 2 illustrates an example of a signal transmissionsequence in the wireless LAN system 100 illustrated in FIG. 1 (note thata horizontal axis is a time axis). While a STA (an OBSS-STA) in the OBSS102 is transmitting a signal, STA 1 to STA 3 are set to a busy state andstand by for transmission until the transmission processing of theOBSS-STA is terminated. On the other hand, even if the OBSS-STA does notcomplete signal transmission, the AP can determine that the AP cantransmit a signal to STA 2. This is because STA 2 exists outside thereceivable range of the OBSS 102, and does not receive interference oronly receives small interference from the OBSS-STA.

By setting an OBSS-PD threshold that is less than the reception power ofa signal from the OBSS-STA, the AP returns to an IDLE state (in otherwords, a non-busy state) after detecting a BSS Color in a PHY header ofthe received signal, and the AP can start the transmission of a signalto STA 2. In contrast, in a case where the AP transmits a signal to STA1 rather than STA 2, it is obvious that a signal received by STA 1 isstrongly interfered with by the OBSS-STA.

Accordingly, in SR transmission based on OBSS-PD, the key to success isto appropriately select a transmission destination of a signal. However,in practice, a wireless LAN is not a centralized system but is adistributed system, and all of the STAs autonomously performcommunication. Therefore, in a case where SR transmission based onOBSS-PD is applied, it is significantly difficult to select anappropriate transmission destination.

SR transmission based on OBSS-PD is defined in the latest IEEE 802.11axspecification, but no prior arts, such as documents, that discuss thedynamic adjustment of an OBSS-PD threshold have not been discovered. Ingeneral, if the OBSS-PD threshold is a fixed value, only a limitedeffect of SR is realized. The most significant obstacle in dynamicallyutilizing SR transmission based on OBSS-PD is that the AP lacksinformation relating to interference from the OBSS that each candidatefor a transmission destination will receive. Therefore, the AP fails tocorrectly determine both whether or not a higher OBSS-PD threshold is tobe set in order to create a transmission opportunity and whichtransmission destination a signal is to be transmitted to.

In order to easily perform dynamic SR transmission based on OBSS-PD, aminimum level of information exchange is required. If a report about aresult of measuring reception power is added to OBSS information, APscan mutually exchange information relating to OBSS interference that aBSS of the local AP is receiving. By doing this, an AP can grasp asituation of another AP, and this enables the performance of theentirety of a system to be optimized while the respective APs cooperatewith each other.

Herein, a method relating to the exchange of information that causesdynamic SR transmission based on OBSS-PD to be easily performed isproposed below.

Example 1

In Example 1, when an AP performs downlink SR transmission based onOBSS-PD, the AP uses a receiving signal strength indicator (RSSI) of anOBSS signal of each STA under control as information for appropriatelyselecting a transmission destination. The RSSI is information that canalmost directly indicates an influence of interference that a STAreceives from an OBSS, and the AP can select a more appropriatetransmission destination. Furthermore, the AP needs a minimum sequence(overhead) to exchange information relating to the RSSI of the OBSS witheach of the STAs under control in order to realize downlink SRtransmission based on OBSS-PD.

FIG. 3 illustrates an example of a configuration of a wireless LANsystem 300 to which the technology disclosed herein can be applied. Inthis drawing, an AP configures a single BSS together with STA 1 to STA 4under control (that are not APs). Furthermore, four OBSS's having anoverlapping receivable range exist to be adjacent to this BSS. Assumethat (BSS Colors of) the respective OBSS's are OBSS 1, OBSS 2, OBSS 3,and OBSS 4. Example 1 of the technology disclosed herein is describedbelow in detail with appropriate reference to FIG. 3.

When a STA of one of the OBSS's is transmitting a signal and terminalstations (STA 1 to STA 4 and the AP) receive a frame, the terminalstations check the field “BSS Color” in a PHY header of the frame so asto identify whether or not the received frame is a frame that hasarrived from the OBSS.

FIG. 4 illustrates a processing procedure performed when a terminalstation receives a frame in the form of a flowchart.

Upon receipt of a frame (step S401), a terminal station checks the field“BSS Color” in a PHY header of the frame (step S402).

First, the terminal station checks whether or not the field “BSS Color”in the PHY header is available (step S403). In a case where atransmission source of the frame does not conform to IEEE 802.11ax, thefield “BSS Color” does not exist in the PHY header, and in other words,the field “BSS Color” is not available.

On the other hand, in a case where the field “BSS Color” in the PHYheader is available (Yes in step S403), the terminal station furtherchecks whether or not the received frame is a frame that has arrivedfrom an OBSS on the basis of whether or not a value of the BSS Color isdifferent from a value of the terminal station (step S404).

Then, in a case where the received frame is a frame that has arrivedfrom the OBSS (Yes in step S404), the terminal station records, forexample, reception power measured in a preamble portion of the receivedframe, namely, an RSSI, together with the value of the BSS Colorobtained in step S403 (step S405).

When a time period has passed, the terminal station can record RSSI'sand BSS Colors from all or most of neighboring OBSS's. However, it is tobe noted that a position and an ambient environment of each of theterminal stations change with time, and therefore each of the terminalstations needs to update the information above relating to the OBSS.

FIG. 5 illustrates an implementation example of a STA that can realizefunctionality relating to downlink SR transmission based on OBSS-PD, asdescribed above, by using the valid complexity of hardware in the formof a block diagram.

A BSS Color detector 501 detects a BSS Color described in a PHY headerof a frame that has arrived. Whether an arrival signal is a BSS signalor an OBSS signal can be determined on the basis of the detected BSSColor. A bank of moving average (MA) filters 502-1, 502-2, . . . , and502-N is arranged in order to process an RSSI of a received signal fromeach of the OBSS's. Once the BSS Color detector 501 specifies the BSSColor of the frame that has arrived, an RSSI of the frame is pushed intoa corresponding MA filter 502-1, 502-2, . . . , or 502-N, and an outputof the corresponding MA filter is labeled a BSS Color of a correspondingOBSS, and is stored in a table (an OBSS RSSI table) 503.

Even a signal from the same transmitter has a large deviation inreception power in some cases. However, by using the MA filters 502-1and the like, the effectiveness of the deviation in reception power canbe reduced due to fading and shadowing. Additionally, the MA filters502-1 and the like can track a change in reception power that isgenerated due to a change in the position or ambient environment of aterminal station, as described above.

Upon receipt of a measurement request from an AP, a STA transmits, tothe AP, information stored in the OBSS RSSI table 503. It is to be notedthat the number of OBSS's is an indefinite value depending on asituation of a BSS or an individual STA, and it is preferable thatminimum information be transmitted instead of all pieces of informationstored in the OBSS RSSI table 503.

Accordingly, a rearrangement/search unit 504 rearranges records of theOBSS RSSI table 503 according to the size of the RSSI, extracts, fromthe OBSS RSSI table 503, maximum value information (Max) that includes apair of a maximum value (RSSI_max) of the RSSI and a BSS Color(Color_max) of a corresponding OBSS, and minimum value information (Min)that includes a pair of a minimum value (RSSI_min) of the RSSI and a BSSColor (Color_min) of a corresponding OBSS, and transmits the maximumvalue information and the minimum value information to the AP.

As described above, the AP transmits the measurement request so as to beable to periodically obtain OBSS RSSI information, as described above,from a specified STA (under control) that is not an AP. After the STAunder the control of the AP receives a measurement request frame fromthe AP, the STA checks the OBSS RSSI table 503, and transmits, to theAP, a measurement report frame that includes the maximum value and theminimum value of the RSSI and information relating to respective pairedBSS Colors.

FIG. 6 illustrates a processing procedure in which the STA under thecontrol of the AP reports the OBSS RSSI information to the AP in theform of a flowchart.

Upon receipt of a measurement request from the AP (step S601), the STAunder the control of the AP checks the OBSS RSSI table 503 (see FIG. 5),and searches for BSS Colors that respectively correspond to the maximumvalue and the maximum value of the RSSI (step S602).

Then, the STA writes the maximum value and the minimum value of the RSSIand the respective paired BSS Colors to a measurement report frame (stepS603), and transmits the measurement report frame to the AP (step S604).

The number of OBSS's is indefinite and depends on a specified situation,and therefore the size of the OBSS RSSI table 503 is variable.Therefore, it is to be noted that it is preferable that a limitedminimum piece of information, rather than the entirety of the table, betransmitted from the STA to the AP. Herein, as described with referenceto FIGS. 5 and 6, it is recommended that the STA only transmit, to theAP, the maximum value and the maximum value of the RSSI and therespective BSS Colors that have been recorded.

FIG. 7 illustrates an example of a configuration of the measurementreport frame. The frame includes a preamble located at the top, aphysical layer convergence protocol (PLCP) header, and an MPDU that isequivalent to a media access control (MAC) frame. Furthermore, the MACprotocol data unit (MPDU) includes a MAC header, a frame body, and aframe check sequence (FCS). In the illustrated frame configurationexample, information relating to a measurement report of reception poweris described in the frame body of the MPDU.

In the frame body, respective fields, Category, Action, and InformationElement, are provided. In the field “Category”, a value indicating anaction to be performed on this frame is set, and the field “Category” isprobably set to 5 in order to mean a frame for wireless measurement. Thefield “Action” is set to 1, and this indicates a measurement reportframe (incidentally, 0 indicates a measurement request frame). In thefield “Information Element”, OBSS RSSI information that includes a pairof a maximum value (Max OBSS RSSI) of an OBSS RSSI to be reported andcolor information (Max OBSS RSSI Color) of the maximum value and a pairof a minimum value (Min OBSS RSSI) of the OBSS RSSI and colorinformation (Min OBSS RSSI Color) of the minimum value, and an elementID used to indicate a measurement report (of reception power) arestored. The OBSS RSSI information is information obtained by pairing anRSSI of a signal of an OBSS and a BSS Color of the OBSS, and may furtherinclude information that is different from the maximum value and theminimum value of the RSSI that are described above.

Note that the STA may transmit the OBSS RSSI information described aboveto the AP by using a management frame or an action frame.

After the AP collects the OBSS RSSI information by using the measurementreport frames transmitted from all of the STAs in a BSS of the AP, theAP can construct a table or a database that reflects a rough positionalrelationship among each of the STAs under control, OBSS's, and the AP.FIG. 8 illustrates an example of the table above. In the illustratedtable, for each of the OBSS's, a STA (Min RSSI) having a minimum RSSIand a STA (Max RSSI) having a maximum RSSI are listed.

Referring to the network configuration illustrated in FIG. 3, STA 2 andSTA 4 are located apart from OBSS 1, and therefore an RSSI from OBSS 1has a minimum value, and STA 2 and STA 4 are listed in the row “Min RSSIof the column OBSS 1 in the table illustrated in FIG. 8. Furthermore,STA 2 is located closest to OBSS 2, and therefore an RSSI from OBSS 2has a maximum value, and STA 2 is listed in the row “Max RSSI” of thecolumn “OBSS 2” in the same table. Furthermore, STA 4 is located closestto OBSS 3, and therefore an RSSI from OBSS 3 has a maximum value, andSTA 4 is listed in the row “Max RSSI” of the column “OBSS 3” in the sametable.

Furthermore, STA 1 is located closest to OBSS 4, an RSSI from OBSS 4 hasa maximum value, and STA 1 is listed in the row “Max RSSI” of the column“OBSS 4” in the same table. In addition, STA 1 is located apart fromOBSS 2, an RSSI from OBSS 2 has a minimum value, and STA 1 is listed inthe row “Min RSSI” of the column “OBSS 2” in the same table.

Furthermore, STA 3 is located closest to OBSS 1, an RSSI from OBSS 1 hasa maximum value, and STA 3 is listed in the row “Max RSSI” of the column“OBSS 1” in the same table. In addition, STA 3 is located apart fromOBSS 3, an RSSI from OBSS 3 has a minimum value, and STA 3 is listed inthe row “Min RSSI” of the column “OBSS 3”.

In brief, the table illustrated in FIG. 8 lists a STA for which an RSSIfrom each of the OBSS's becomes minimum or maximum on the basis of themeasurement report frame that the AP has received from each of the STAsunder control. A table having the structure above reflects a roughpositional relationship among each of the STAs under the control of anAP, OBSS's, and the AP, and can also be said to reflect degrees ofinterference that each of the STAs under the control of the AP receivesfrom the OBSS's.

Note that under a communication environment where the transmittance ofradio waves is uniform, the RSSI is almost proportional to a distancebetween transceivers. Therefore, a table that is constructed on thebasis of RSSI's from OBSS's, as illustrated in FIG. 8, can be said toindicate a positional relationship among each of the STAs under thecontrol of an AP, the OBSS's, and the AP. On the other hand, under acommunication environment where an obstacle having a low transmittanceof radio waves (such as a screen door, a window glass, or the like) isdistributed, there is a possibility that an RSSI that is lower than anRSSI to be expected from an actual distance will be measured for a STAthat an OBSS signal arrives at via the obstacle. However, even if atable is constructed on the basis of an RSSI that does not reflect anactual positional relationship with a STA or an OBSS due to the presenceof the obstacle, it is thought that no problem arises in the viewpointof avoiding interference with an OBSS signal and realizing SRtransmission.

FIG. 9 explains an example of a method in which an AP utilizes the tableillustrated in FIG. 8 so as to realize SR transmission based on OBSS-PDin the wireless LAN system 300 illustrated in FIG. 3. Furthermore, FIG.10 illustrates an example of a signal transmission sequence at a timewhen a signal has been transmitted from OBSS 2 (note that a horizontalaxis is a time axis).

When a signal has arrived from OBSS 2, the AP is temporarily set to abusy state, and stands by for transmission. At this time, when the APdetects that the field “BSS Color” in a PHY header of a frame receivedfrom OBSS 2 is available and that the received signal is a signal thathas arrived from OBSS 2 (OBSS Color filtering), the AP makes an attemptto realize SR transmission based on OBSS-PD (by setting an appropriateOBSS-PD threshold, for example, by increasing an OBSS-PD threshold). Inother words, the AP refers to the category “Min RSSI” of OBSS 2 in thetable illustrated in FIG. 8, and senses that an OBSS 2 signal having aminimum RSSI arrives at STA 1 at this point in time. Accordingly, the APcan determine to perform SR transmission to STA 1 for which interferencereceived from OBSS 2 is smaller than interference of the other STAsbecause STA 1 is located apart from OBSS 2.

Furthermore, FIG. 11 explains another example of the method in which theAP utilizes the table illustrated in FIG. 8 so as to realize SRtransmission based on OBSS-PD in the wireless LAN system 300 illustratedin FIG. 3. FIG. 12 illustrates an example of a signal transmissionsequence at a time when a signal has been transmitted from OBSS 1 (notethat a horizontal axis is a time axis). The AP is temporarily set to abusy state, and stands by for transmission. The AP also refers to a PHYheader of a received frame, and detects that the received signal is asignal that has arrived from OBSS 1. Then, the AP refers to the category“Min RSSI” of OBSS 1 in the table illustrated in FIG. 8, and senses thatan OBSS 1 signal having a minimum RSSI arrives at STA 2 and STA 4 atthis point in time. Accordingly, the AP can determine to perform SRtransmission to STA 2 or STA 4 because STA 2 and STA 4 are located apartfrom OBSS 1. At this time, the AP may determine which of STA 2 and STA 4transmission is to be performed on in accordance with a certain standardsuch as an original queue sequence or a priority order.

Furthermore, in a method for configuring a table on the basis of themeasurement report frames received from STAs under control, it is alsoassumed that an OBSS for which the category “Min RSSI” becomes blankexists, for example, as illustrated as OBSS 4 in the table illustratedin FIG. 8. In such a case, the AP may make an attempt to perform SRtransmission to one of STAs that an OBSS 4 signal that does not have amaximum RSSI arrives at. In a case where OBSS 4 is transmitting a signal(see FIGS. 13 and 14), the AP is temporarily set to a busy state, andstands by for transmission. The AP also refers to a PHY header of areceived frame, and detects that the received signal is a signal thathas arrived from OBSS 4. Then, the AP refers to the category “Min RSSI”of OBSS 4 in the table illustrated in FIG. 8, and fails to sense a STAthat an OBSS 4 signal having a minimum RSSI arrives at this point intime. However, the AP refers to the category “Max RSSI” of OBSS 4 in thesame table, and can discover that STA 1 is located closest to OBSS 4.Accordingly, the AP can determine to perform SR transmission to a STAother than STA 1, namely, one of STA 2 to STA 4. At this time, the APmay determine which of STA 2 to STA 4 transmission is to be performed onin accordance with a certain standard such as an original queue sequenceor a priority order.

FIG. 15 illustrates a processing procedure in which an AP realizes SRtransmission based on OBSS-PD by utilizing the table illustrated in FIG.8 (that has been constructed on the basis of the measurement reports ofreception power from STAs under control) in the form of a flowchart.

Upon receipt of a frame (step S1501), the AP checks the field “BSSColor” in a PHY header of the frame (step S1502).

First, the AP checks whether or not the field “BSS Color” in the PHYheader is available (step S1503). In a case where a transmission sourceof the frame does not conform to IEEE 802.11ax, the field “BSS Color”does not exist in the PHY header, and in other words, the field “BSSColor” is not available.

On the other hand, in a case where the field “BSS Color” in the PHYheader is available (Yes in step S1503), the AP further checks whetheror not the received frame is a frame that has arrived from an OBSS onthe basis of whether or not a value of the BSS Color is different from avalue of the AP (step S1504).

Then, in a case where the received frame is a frame that has arrivedfrom the OBSS (Yes in step S1504), when the AP confirms that an RSSI ofa signal of the OBSS is greater than or equal to a minimum value(OBSS-PD Thld_min) of an OBSS-PD threshold and is less than or equal toa maximum value (OBSS-PD Thld_max) of the OBSS-PD threshold (Yes in stepS1505), the AP sets an appropriate OBSS-PD threshold, and also stopsprocessing for receiving the OBSS frame (step S1506).

Next, the AP checks a database (for example, the table illustrated inFIG. 8 that has been constructed on the basis of the measurement reportsof reception power from STAs under control), and searches for a STAhaving a minimum RSSI with respect to a BSS Color (identified in stepS1503) of an OBSS signal that has currently arrived (step S1507).

Here, in a case where a STA having a minimum RSSI with respect to theBSS Color of a current arrival frame has been discovered and the AP hastransmission data for the STA (Yes in step S1508), the AP moves thediscovered STA to the top of a transmission queue (step S1509).

On the other hand, in a case where a STA having a minimum RSSI withrespect to the BSS Color of the current arrival frame has not beendiscovered (No in step S1508), the AP further checks the database, andsearches for a STA that does not exist in the category “Max RSSI” withrespect to the BSS Color of the current arrival frame (step S1510).

Then, in a case where a STA that does not exist in the category “MaxRSSI” with respect to the BSS Color of the current arrival frame hasbeen discovered and the AP has transmission data for the STA (Yes instep S1511), the AP moves the discovered STA to the top of atransmission queue (step S1509).

Thereafter, the AP restarts backoff (step S1512). Then, in a case wherea backoff time has elapsed but the frame that has arrived in step S1501has not yet been finished (Yes in step S1513), the AP sets anappropriate transmission power, and transmits a packet (step S1514).

As described above, when the AP performs downlink SR transmission basedon OBSS-PD, the AP uses an RSSI of an OBSS signal of each of the STAsunder control as information for appropriately selecting a transmissiondestination. The RSSI is information that can almost directly indicatesan influence of interference that a STA receives from an OBSS, and theAP can select a more appropriate transmission destination. However, theAP needs a minimum sequence (overhead) to exchange information relatingto the RSSI of the OBSS with each of the STAs under control in order torealize downlink SR transmission based on OBSS-PD.

Example 2

In Example 2, when the AP performs downlink SR transmission based onOBSS-PD, the AP uses information relating to an angle of arrival (AoA)as information for appropriately selecting a transmission destination.The AoA itself does not directly indicate an influence of aninterference signal. However, an influence of interference that a STAreceives from an OBSS also changes according to a degree of similarityin the AoA to an OBSS signal, and therefore the AP can utilize the AoAas information for selecting a candidate for the transmissiondestination.

Then, the AP uses the measurement of AoA's of a BSS signal and the OBSSsignal by spontaneously using a directional antenna without obtaininginformation such as the OBSS RSSI information (described above) fromeach of the STAs under control so as to be able to generate a table thatreflects a rough positional relationship among each of the STAs undercontrol, OBSS's, and the AP. This enables exchange of information withthe STAs or the like to be omitted. Such a table reflects a roughpositional relationship between the STAs and the OBSS's, and can also besaid to reflect degrees of interference that each of the STAs under thecontrol of the AP receives from the OBSS's.

In a wireless LAN system 1600 illustrated in FIG. 16, an AP configures asingle BSS together with STA 1 to STA 4 under control (that are notAPs). Furthermore, two OBSS's, OBSS 1 and OBSS 2, are adjacent to thisBSS. The AP can obtain AoA's of STA 1 to STA 4 under control, OBSS 1,and OBSS 2 by using AoA measurement by spontaneously using a directionalantenna. The AP uses MA processing that is similar to MA processingillustrated in FIG. 5 so as to reduce the effectiveness of a deviationin reception power due to fading and shadowing, and obtains an averageAoA of STA 1 to STA 4, OBSS 1, and OBSS 2. However, the AP may obtainAoA's of each of the STAs under control and the OBSS's by using anarbitrary method other than spontaneous measurement.

After data of the AoA becomes available, the AP divides a space into aplurality of clusters (four clusters 1 to 4 in the illustrated example),as illustrated in FIG. 17, performs clustering processing for groupingSTAs and an OBSS that have a similar AoA into the same cluster, andclassifies the wireless LAN system 1600 each of the STAs and the OBSS'sinto clusters different from each other.

As described above, the AP can generate a table in which the STAs undercontrol and the OBSS's have been classified into clusters 1 to 4 on thebasis of the AoA, as illustrated in FIG. 18. AoA's of signals thatarrive at the AP from STA 1, STA 3, and OBSS 1 are similar to eachother, and therefore STA 1, STA 3, and OBSS 1 are grouped into cluster1. Furthermore, AoA's of signals that arrive at the AP from STA 2 andOBSS 2 are similar to each other, and therefore STA 2 and OBSS 2 aregrouped into cluster 3. On the other hand, there are neither STAs norOBSS's that belong to cluster 2, and only STA 4 exists in cluster 4. ASTA and an OBSS in the same cluster mean to have a similar angle ofarrival at the AP, and it is also understood from FIG. 17 that the STAand the OBSS in the same cluster are physically close to each other. Incontrast, it is also understood from FIG. 17 that there is a possibilitythat a STA and an OBSS that respectively belong to clusters in whichangles of arrival at the AP are located on sides opposite to each otherare physically located apart from each other.

For example, when OBSS 1 is transmitting a signal, as illustrated inFIG. 17, the AP can understand that STA 1 and STA 3 belong to cluster 1serving as the same cluster as a cluster that OBSS 1 belongs to, bysearching the table illustrated in FIG. 18. Accordingly, because thereis a possibility that OBSS 1 is physically close to each of STA 1 andSTA 3, the AP may avoid transmission to STA 1 and STA 3, and may performSR transmission to STA 2 that belongs to cluster 3 that is located at anAoA opposite to an AoA of cluster 1.

Note that FIG. 17 illustrates an example where 360 degrees around the APare equally divided into four clusters at each AoA of 90 degrees, but donot need to be divided into clusters at each identical AoA. For example,a direction in which OBSS's and STAs exist in high density may bedivided into clusters at each narrow AoA. In contrast, in a direction inwhich OBSS's and STAs exist in low density, the STAs and the OBSS's maybe grouped into a single cluster by using a wide AoA. Furthermore,cluster division may be performed in such a way that an almost equalnumber of OBSS's and STAs are accommodated in each of the clusters, orcluster division may be performed in such a way that OBSS's aredistributed.

Furthermore, FIGS. 17 and 18 illustrate an example where thecircumference of the AP is divided into four clusters, but thecircumference of the AP can be divided into three or less clusters, ormay be divided into five or more clusters.

In brief, the table illustrated in FIG. 18 lists clusters obtained byperforming clustering processing on STAs and OBSS's on the basis of anangle of arrival at the AP. A STA and an OBSS in the same cluster have asimilar AoA, and therefore the STA and the OBSS are physically close toeach other. There is a possibility that an influence of interference issignificant. In contrast, a STA and an OBSS that respectively belong toclusters in which angles of arrival at the AP are located opposite toeach other are physically located apart from each other, and there is apossibility that an influence of interference is small. Accordingly, thecluster table described above reflects a rough positional relationshipamong each of the STAs under the control of an AP, OBSS's, and the AP,and can also be said to reflect degrees of interference that each of theSTAs under the control of the AP receives from the OBSS's.

Note that radio waves that arrive at the AP from a STA or an OBSS arenot limited to direct waves, and there is a possibility that the radiowaves are reflected waves that have been reflected by a wall or the likeor other indirect waves. If arrival waves of the AP are not directwaves, a STA or an OBSS serving as a signal source of the arrival wavesdoes not exist in a direction of an AoA measured in the AP, and a tableobtained by performing clustering processing on the basis of the arrivalwaves does not necessarily reflect an actual positional relationshipwith the STA or the OBSS. However, if radio waves propagate through thesame route in a going path and a returning path and sending-out isperformed in a direction of an AoA, it can be assumed that a signal istransmitted to a corresponding party. Accordingly, even if a clustertable that does not reflect an actual positional relationship isconstructed on the basis of an AoA of arrival waves including indirectwaves, it is thought that no problem arises in the viewpoint of avoidinginterference with an OBSS signal and realizing SR transmission.

FIG. 19 illustrates a processing procedure in which an AP realizes SRtransmission based on OBSS-PD by utilizing the table illustrated in FIG.18 (that has been constructed on the basis of AoA's of a STA and anOBSS) in the form of a flowchart.

Upon receipt of a frame (step S1901), the AP checks the field “BSSColor” in a PHY header of the frame (step S1902).

First, the AP checks whether or not the field “BSS Color” in the PHYheader is available (step S1903). In a case where a transmission sourceof the frame does not conform to IEEE 802.11ax, the field “BSS Color”does not exist in the PHY header, and in other words, the field “BSSColor” is not available.

On the other hand, in a case where the field “BSS Color” in the PHYheader is available (Yes in step S1903), the AP further checks whetheror not the received frame is a frame that has arrived from an OBSS onthe basis of whether or not a value of the BSS Color is different from avalue of the AP (step S1904).

Then, in a case where the received frame is a frame that has arrivedfrom the OBSS (Yes in step S1904), when the AP confirms that an RSSI ofa signal of the OBSS is greater than or equal to a minimum value(OBSS-PD Thld_min) of an OBSS-PD threshold and is less than or equal toa maximum value (OBSS-PD Thld_max) of the OBSS-PD threshold (Yes in stepS1905), the AP sets an appropriate OBSS-PD threshold, and also stopsprocessing for receiving the OBSS frame (step S1906).

Next, the AP checks a database (for example, the table illustrated inFIG. 18 that has been constructed by performing clustering on a STA andan OBSS on the basis of an AoA), and searches for a STA that belongs toa cluster that is located on an opposite side of a cluster that an OBSSfrom which an interference signal has currently arrived belongs to (stepS1907).

Here, in a case where a STA that belongs to a cluster that is located onan opposite side of the cluster that the OBSS from which an interferencesignal has currently arrived belongs to has been discovered and the APhas transmission data for the STA (Yes in step S1908), the AP moves thediscovered STA to the top of a transmission queue (step S1909).

On the other hand, in a case where a STA that belongs to a cluster thatis located on an opposite side of the cluster that the OBSS from whichan interference signal has currently arrived belongs to has not beendiscovered (No in step S1908), the AP further checks the database, andsearches for a STA that belongs to a cluster that is different from (islocated as far as possible from) the cluster that the OBSS from which aninterference signal has currently arrived belongs to (step S1910).

Then, in a case where a STA that belongs to a cluster that is differentfrom (is located as far as possible from) the cluster that the OBSS fromwhich an interference signal has currently arrived belongs to has beendiscovered and the AP has transmission data for the STA (Yes in stepS1911), the AP moves the discovered STA to the top of a transmissionqueue (step S1909).

Thereafter, the AP restarts backoff (step S1912). Then, in a case wherea backoff time has elapsed but the frame that has arrived in step S1901has not yet been finished (Yes in step S1913), the AP sets anappropriate transmission power, and transmits a packet (step S1914).

As described above, when the AP performs downlink SR transmission basedon OBSS-PD, the AP uses information relating to AoA's of STAs undercontrol and OBSS's as information for appropriately selecting atransmission destination. The AoA itself does not directly indicate aninfluence of an interference signal. However, an influence ofinterference that a STA receives from an OBSS also changes according toa degree of similarity in the AoA to an OBSS signal, and therefore theAP can utilize the AoA as information for selecting a candidate for thetransmission destination. Furthermore, the AP can measure AoA's ofsignals that arrive from the STAs under control and the OBSS's byspontaneously using a directional antenna. Accordingly, the AP canselect an appropriate transmission destination on the basis ofinformation relating to the AoA without exchanging information with theSTAs under control, or the like.

Note that the method described in Example 2 for performing downlink SRtransmission based on OBSS-PD can also be used in combination with themethod described in Example 1.

FIG. 20 illustrates an example of a functional configuration of acommunication apparatus 2000 that performs a communication operation asan AP or a STA in Examples 1 and 2 described above. It should beunderstood that both the AP and the STA have a similar basicconfiguration.

The communication apparatus 2000 includes a data processing unit 2001, acontroller 2002, a communication unit 2003, and a power source 2004.Furthermore, the communication unit 2001 further includes amodulator/demodulator 2011, a spatial signal processing unit 2012, achannel estimator 2013, a wireless interface (IF) 2014, an amplifier2015, and an antenna 2016. However, a set of the wireless interface2014, the amplifier 2015, and the antenna 2016 may configure a singletransmission/reception branch, and the communication unit 2001 mayinclude two or more transmission/reception branches. Furthermore, afunction of the amplifier 2015 is included in the wireless interface2014 in some cases.

At the time of transmission of data that has been input from a protocolupper layer (not illustrated), the data processing unit 2001 generates apacket for wireless transmission from the data, performs processing suchas the addition of a header for MAC processing or the addition of anerror detection code, and provides data after processing to themodulator/demodulator 2011. Furthermore, at the time of reception atwhich an input is performed from the modulator/demodulator 2011, thedata processing unit 2001 performs analysis of a MAC header, thedetection of a packet error, reordering processing, and the like, andprovides data after processing to a protocol upper layer of the dataprocessing unit 2001.

The controller 2002 communicates information with each unit in thecommunication apparatus 2000. Furthermore, the controller 2002 performsparameter setting in the modulator/demodulator 2011 and the spatialsignal processing unit 2012 and packet scheduling (the management of atransmission queue, and the like) in the data processing unit 2001.Furthermore, the controller 2002 performs parameter setting andtransmission power control in the wireless interface 2014 and theamplifier 2015.

In a case where the communication apparatus 2000 operates as an AP, thecontroller 2002 controls SR transmission based on an OBSS-PD threshold.

Furthermore, in a case where the communication apparatus 2000 operatesas an AP in Example 1, the controller 2002 processing for transmitting ameasurement request frame to STAs under control, sums a measurementreport frame transmitted from each of the STAs, and constructs a tableor a database (see FIG. 8) that indicates a rough positionalrelationship among each of the STAs under control, OBSS's, and the AP bybeing used in RSSI information, on the basis of OBSS RSSI information.Then, when the controller 2002 detects an OBSS signal, the controller2002 refers to the table or database described above, selects anappropriate STA on which SR transmission will be performed, and controlspacket transmission in accordance with the processing procedureillustrated in FIG. 15.

Furthermore, in a case where the communication apparatus 2000 operatesas a STA in Example 1, the controller 2002 stores a pair of an RSSImeasured for each of the received OBSS signals and a BSS Color of eachof the OBSS's (see FIG. 5). Then, upon receipt of a measurement requestframe from the AP, the controller 2002 controls the transmission of ameasurement report frame (see FIG. 7) storing OBSS RSSI information thatincludes a pair of a maximum value of an OBSS RSSI and correspondingcolor information and a pair of a minimum value of the OBSS RSSI andcorresponding color information.

Furthermore, in a case where the communication apparatus 2000 operatesas an AP in Example 2, the controller 2002 performs clusteringprocessing on the basis of a measurement result of AoA's of signals thatarrive from STAs under control and OBSS's, groups STAs and OBSS's havinga similar AoA into a cluster, and constructs a table or a database (seeFIG. 18) that indicates a rough positional relationship among each ofthe STAs under control, the OBSS's, and the AP by using clusters. Then,when the controller 2002 detects an OBSS signal, the controller 2002refers to the table or database described above, selects an appropriateSTA on which SR transmission will be performed, and controls packettransmission in accordance with the processing procedure illustrated inFIG. 19.

At the time of transmission, the modulator/demodulator 2011 performsencoding, interleaving, and modulation processing on an input data fromthe data processing unit 2001 in accordance with a coding and modulationmethod that has been set by the controller 2001, generates a data symbolstream, and provides the data symbol stream to the spatial signalprocessing unit 2012. Furthermore, at the time of reception, themodulator/demodulator 2011 performs processing, such as demodulation,deinterleaving, or decoding, that is inverse to processing at the timeof transmission on an input from the spatial signal processing unit 2012in accordance with a coding and modulation method set by the controller2001, and provides data to the data processing unit 2001 or thecontroller 2002.

At the time of transmission, the spatial signal processing unit 2012performs signal processing provided for spatial separation on an inputfrom the modulator/demodulator 2011 as needed, and provides one or moreobtained transmission symbol streams to respective wireless interfaces2014. On the other hand, at the time of reception, the spatial signalprocessing unit 2012 performs signal processing on reception symbolstreams that have been input from the respective wireless interfaces2014, spatially resolves the streams as needed, and provides the streamsto the modulator/demodulator 2011.

The channel estimator 2013 calculates complex channel gain informationof a propagation path from preamble portions and training signalportions of input signals from the respective wireless interfaces 2014.Then, the calculated complex channel gain information is used indemodulation processing of the modulator/demodulator 2011 and spatialprocessing of the spatial signal processing unit 2012 via the controller2002, so that spatial multiplex communication such as MIMO can beperformed.

At the time of transmission, the wireless interface 2014 converts aninput from the spatial signal processing unit 2012 into an analogsignal, performs filtering and up-conversion to a carrier frequency, andsends out the analog signal to the antenna 2016 or the amplifier 2015.On the other hand, at the time of reception, the wireless interface 2014performs processing, such as down-conversion or conversion into adigital signal, that is inverse to processing at the time oftransmission on an input (a received signal having the carrierfrequency) from the antenna 2016 or the amplifier 2015, and providesdata to the spatial signal processing unit 2012 and the channelestimator 2013.

In a case where the communication apparatus 2000 operates as a STA inExample 1, the wireless interface 2014 includes a bank of MA filters tomeasure an RSSI of an OBSS signal and obtain a moving average of theRSSI.

At the time of transmission, the amplifier 2015 amplifies the analogsignal that has been input from the wireless interface 2014 to aprescribed power, and sends out the analog signal to the antenna 2016.Furthermore, at the time of reception, the amplifier 2015 performslow-noise amplification on a received signal that has been input fromthe antenna 2016 to a prescribed power, and outputs the received signalto the wireless interface 2014. At least one of a function at the timeof transmission or a function at the time of reception of the amplifier2015 that is described above is included in the wireless interface 2014in some cases.

In a case where the communication apparatus 2000 operates as an AP inExample 2, the antenna 2016 is a directional antenna, and the wirelessinterface 2014 measures AoA's of signals that arrive from STAs undercontrol and OBSS's. Furthermore, the wireless interface 2014 includes abank of MA filters to obtain a moving average of the AoA's.

The power source 2004 includes a battery power source or a fixed powersource such as a commercial power source, and supplies power for drivingto each of the units in the communication apparatus 2000.

Note that the communication apparatus 2000 can further include afunction module other than illustrated units. However, this is notdirectly associated with the technology disclosed herein, andillustration and a description are omitted here.

According to the technology disclosed herein, the following effects areexpected.

(1) STAs can report, to an AP, reception power measurement results froman OBSS, and the AP can perform a communication operation based onOBSS-PD by using these pieces of information, and can perform SRtransmission to a STA having the smallest interference with the OBSS.Alternatively, the AP can perform a communication operation based onOBSS-PD by using information obtained by performing clusteringprocessing on STAs under control and an OBSS on the basis of AoA's, andcan transmit a signal to a STA that is estimated to belong to a clusteron an opposite side of a cluster of the OBSS and to be located apartfrom the OBSS. In brief, the AP can simply determine a STA that isunlikely to receive interference from the OBSS, and can increase anopportunity to perform transmission to a STA.

(2) The communication operation in (1) described above results inimprovements in a spatial reuse rate based on OBSS-PD. Furthermore, theAP transmits a signal to a STA having the smallest interference with theOBSS, and this also results in improvements in a success rate oftransmission.

(3) The AP can acquire more transmission opportunities, and thisprincipally results in improvements in a downlink throughput in awireless LAN system.

(4) The AP can obtain information required to realize downlink SRtransmission based on OBSS-PD by exchanging minimum information withSTAs under control (for example, by transmitting a measurement requestframe and receiving a measurement report frame) or by performing minimummeasurement (for example, the measurement of an AoA), and this resultsin a small overhead.

INDUSTRIAL APPLICABILITY

The technology disclosed herein has been described above in detail withreference to specified embodiments. However, it is obvious that thoseskilled in the art could make modifications or substitutions to theembodiments without departing from the gist of the technology disclosedherein.

The technology disclosed herein is suitably applicable to, for example,a wireless LAN system that conforms to the IEEE 802.11ax standard, butan application range of the technology disclosed herein is not limitedto this. The technology disclosed herein is applicable to variousnetwork systems such as a wireless LAN system in which an AP performsdownlink signal transmission to a STA while permitting interference or awireless LAN system in which a terminal station (regardless of whetheror not it is an AP or a STA) performs one-to-one signal transmissionwhile permitting interference.

In brief, the technology disclosed herein has been described in the formof an example, and the content described herein is not to be construedto be restrictive. In order to determine the gist of the technologydisclosed herein, the claims should be considered.

Note that the technology disclosed herein can also employ theconfiguration described below.

(1) A communication apparatus including:

a communication unit that transmits or receives a signal;

an information obtaining unit that obtains information relating tointerference that each transmission destination candidate receives froman interference source; and

a controller that selects each of the transmission destinationcandidates on the basis of the information when an interference signalarrives.

(2) The communication apparatus described in (1) described above,

in which the controller identifies whether or not the interferencesignal has arrived from an OBSS on the basis of BSS identificationinformation described in a PHY header of a received frame.

(3) The communication apparatus described in (2) described above,

in which the BSS identification information includes a BSS Coloerdefined by IEEE 802.11.

(4) The communication apparatus described in any of (1) to (3) describedabove,

in which the communication apparatus operates as an access point, and

the information obtaining unit obtains the information relating torespective terminal stations serving as each of the transmissiondestination candidates in a local BSS and interference received from anOBSS serving as the interference source.

(5) The communication apparatus described in (4) described above,

in which when a reception power of an OBSS signal serving as theinterference signal is less than or equal to a prescribed threshold, thecontroller selects one of the respective terminal stations in the localBSS on the basis of the information, and causes the signal to betransmitted.

(6) The communication apparatus described in any of (1) to (5) describedabove,

in which the controller selects a transmission destination candidatethat the information indicates that is located farthest from theinterference source that corresponds to the interference signal or isnot located closest to the interference source.

(7) The communication apparatus described in any of (1) to (5) describedabove,

in which the information obtaining unit obtains the information relatingto an intensity of a received signal from the interference source ofeach of the transmission destination candidates, and

the controller selects each of the transmission destination candidateson the basis of the intensity of the received signal from theinterference source that corresponds to the interference signal.

(8) The communication apparatus described in (7) described above,

in which the controller selects a transmission destination candidatethat the information indicates that has a lowest intensity of thereceived signal from the interference source that corresponds to theinterference signal or does not have a highest intensity of the receivedsignal from the interference source.

(9) The communication apparatus described in any of (7) and (8)described above,

in which the information obtaining unit obtains the information on thebasis of a report relating to the intensity of the received signal fromthe interference source, the report being transmitted from each of thetransmission destination candidates.

(10) The communication apparatus described in any of (7) to (9)described above,

in which the information obtaining unit obtains the information on thebasis of a report relating to a measurement result of the intensity ofthe received signal from the interference source, the report beingtransmitted by each of the transmission destination candidates inresponse to a measurement request from a local station.

(11) The communication apparatus described in any of (7) to (10)described above,

in which the communication apparatus operates as an access point,

the information obtaining unit obtains the information relating to theintensity of the received signal of an OBSS signal in each terminalstation serving as each of the transmission destination candidates in alocal BSS, and

the controller manages the information of each of the terminal stationsin association with BSS identification information of an OBSS.

(12) The communication apparatus described in (11) described above,

in which the information obtaining unit obtains, from each of theterminal stations, the information including the BSS identificationinformation that indicates at least one of an OBSS having a maximumintensity of the received signal or an OBSS having a minimum intensityof the received signal.

(13) The communication apparatus described in any of (1) to (11)described above,

in which the information obtaining unit obtains the information relatingto an angle of arrival of each of the transmission destinationcandidates and the interference source, and

the controller selects each of the transmission destination candidateson the basis of a relationship of the angle of arrival between theinterference source that corresponds to the interference signal and eachof the transmission destination candidates.

(14) The communication apparatus described in (13) described above,

in which the controller selects a transmission destination candidatethat the information indicates that is most different in the angle ofarrival from the interference source that corresponds to theinterference signal or is not most similar in the angle of arrival tothe interference source.

(15) The communication apparatus described in any of (13) and (14)described above,

in which the communication unit includes a directional antenna, and

the information obtaining unit obtains the information relating to theangle of arrival on the basis of a result of receiving signals from eachof the transmission destination candidates and the interference sourceby using the directional antenna.

(16) The communication apparatus described in any of (13) to (15)described above,

in which the communication apparatus operates as an access point,

the information obtaining unit obtains the information relating to theangle of arrival of terminal stations serving as each of thetransmission destination candidates in a local BSS and OBSS's, and

the controller groups terminal stations and an OBSS that are similar inthe angle of arrival into a cluster, and manages respective clusters inassociation with the BSS identification information of each of theOBSS's.

(17) A communication method including:

an information obtaining step of obtaining information relating tointerference that each transmission destination candidate receives froman interference source; and

a controlling step of selecting each of the transmission destinationcandidates on the basis of the information when an interference signalarrives.

(18) A communication apparatus that operates under a control of anaccess point, the communication apparatus including:

a controller that performs control to transmit, to the access point,information relating to an intensity of a received signal of an OBSSsignal.

(18-1) The communication apparatus described in (18) described above,further including:

a measuring unit that identifies the OBSS signal on the basis of BSSidentification information described in a PHY header of a receivedframe, and measures an intensity of a received signal of the OBSSsignal.

(19) The communication apparatus described in (18) described above,

in which the controller performs control to transmit, to the accesspoint, the information that associates the intensity of the receivedsignal of the OBSS signal with BSS identification information of anOBSS.

(20) The communication apparatus described in any of (18) and (19)described above,

in which the controller performs control to transmit, to the accesspoint, the information including the BSS identification information thatindicates at least one of an OBSS having a maximum intensity of thereceived signal or an OBSS having a minimum intensity of the receivedsignal.

(21) The communication apparatus described in any of (18) to (20)described above,

in which the controller causes a report frame to be transmitted to theaccess point in response to a request frame from the access point, thereport frame including the information.

(22) A communication method in a communication apparatus that operatesunder a control of an access point, the communication method including:

a controlling step of performing control to transmit, to the accesspoint, information relating to an intensity of a received signal of anOBSS signal.

REFERENCE SIGNS LIST

-   100 Wireless LAN system-   101 BSS-   102 OBSS-   300 Wireless LAN system-   501 BSS Color detector-   502-1, 502-2, . . . , 502-N MA filter-   503 OBSS RSSI table-   504 Rearrangement/search unit-   1600 Wireless LAN system-   2000 Communication apparatus-   2001 Data processing unit-   2002 Controller-   2003 Communication unit-   2004 Power source-   2011 Modulator/demodulator-   512 Spatial signal processing unit-   2013 Channel estimator-   2014 Wireless interface-   2015 Amplifier-   2016 Antenna

The invention claimed is:
 1. A communication apparatus, comprising: circuitry configured to: transmit or receive a signal; obtain first information for each of a plurality of transmission destination candidates, wherein the first information is related to an angle of arrival between each of the plurality of transmission destination candidates and an interference source, and the interference source corresponds to an interference signal; and select a first transmission destination candidate from the plurality of transmission destination candidates based on the first information, wherein the first information indicates that the first transmission destination candidate is one of most different in the angle of arrival of the interference signal from the interference source or not most similar in the angle of arrival of the interference signal from the interference source.
 2. The communication apparatus according to claim 1, wherein the circuitry is further configured to identify arrival of the interference signal from an overlapping basic service set (OBSS) based on basic service set (BSS) identification information, and the BSS identification information is in a PHY header of a received frame.
 3. The communication apparatus according to claim 2, wherein the BSS identification information includes a BSS Color defined by IEEE 802.11.
 4. The communication apparatus according to claim 1, wherein the communication apparatus is configured to operate as an access point, the circuitry is further configured to obtain second information for each of the plurality of transmission destination candidates, and the second information is related to: each terminal station of a plurality of terminal stations, wherein each terminal station serves as a respective transmission destination candidate of the plurality of the transmission destination candidates in a local basic service set (BSS) and the interference signal received from an overlapping basic service set (OBSS) that serves as the interference source.
 5. The communication apparatus according to claim 4, wherein the circuitry is further configured to obtain third information for each of the plurality of transmission destination candidates, the third information is related to a reception power of an OBSS signal that serves as the interference signal, the reception power is less than or equal to a threshold, and the circuitry is further configured to: select one terminal station of the plurality of terminal stations in the local BSS based on the third information related to the reception power of the OBSS signal, and transmit the signal.
 6. The communication apparatus according to claim 1, wherein the circuitry is further configured to select a second transmission destination candidate from the plurality of transmission destination candidates based on second information, the second information indicates that a distance of the selected second transmission destination candidate from the interference source is maximum among distances of the plurality of transmission destination candidates from the interference source.
 7. The communication apparatus according to claim 1, wherein the circuitry is further configured to obtain second information for each of the plurality of transmission destination candidates, the second information is related to an intensity of a signal of a plurality of signals received from the interference source, the interference source is associated with each of the plurality of transmission destination candidates, the circuitry is further configured to select each of the plurality of transmission destination candidates based on the intensity of the signal received from the interference source, and the signal received from the interference source corresponds to the interference signal.
 8. The communication apparatus according to claim 7, wherein the circuitry is further configured to select a second transmission destination candidate from the plurality of the transmission destination candidates based on third information, the third information indicates that an intensity of a specific signal associated with the selected second transmission destination candidate is lowest among intensities of the plurality of signals received from the interference source, the plurality of signals includes the specific signal, and the specific signal is received from the interference source.
 9. The communication apparatus according to claim 7, wherein the circuitry is further configured to obtain third information for each of the plurality of transmission destination candidates based on a report related to the intensity of the received signal, and each of the plurality of transmission destination candidates transmits the report.
 10. The communication apparatus according to claim 7, wherein the circuitry is further configured to obtain third information based on a report related to a measurement result of the intensity of the received signal, and each of the plurality of transmission destination candidates is configured to transmit the report based on a measurement request from a local station.
 11. The communication apparatus according to claim 7, wherein the communication apparatus is configured to operate as an access point, the circuitry is further configured to obtain third information for each of the plurality of transmission destination candidates, the third information is related to the intensity of the received signal in each terminal station of a plurality of terminal stations, the received signal is an overlapping basic service set (OBSS) signal, each terminal station serves as each of the plurality of transmission destination candidates in a local basic service set (BSS), and the circuitry is further configured to manage the third information of each terminal station of the plurality of terminal stations in association with BSS identification information of an OBSS.
 12. The communication apparatus according to claim 11, wherein the circuitry is further configured to obtain, from each of the plurality of terminal stations, fourth information that includes the BSS identification information, the BSS identification information indicates one of a first OBSS signal of a plurality of OBSS signals with a first intensity or a second OBSS signal of the plurality of OBSS signals with a second intensity, the first intensity of the first OBSS signal is maximum among intensities of the plurality of OBSS signals, and the second intensity of the second OBSS signal is minimum among the intensities of the plurality of OBSS signals.
 13. The communication apparatus according to claim 1, wherein the circuitry includes a directional antenna, the circuitry is further configured to obtain the first information related to the angle of arrival based on a result of a plurality of signals received from the plurality of transmission destination candidates and the interference source, and the first information is obtained by the directional antenna.
 14. The communication apparatus according to claim 1, wherein the communication apparatus is configured to operate as an access point, the circuitry is further configured to: obtain second information related to an angle of arrival of a plurality of terminal stations serving as the plurality of transmission destination candidates in a local BSS and a plurality of overlapping basic service set (OBSS), group the plurality of terminal stations and an OBSS of the plurality of OBSS that are same in the angle of arrival into a cluster, and manage respective clusters in association with BSS identification information of each of the plurality of OBSS.
 15. A communication method, comprising: transmitting or receiving, by circuitry, a signal; obtaining, by the circuitry, information for each of a plurality of transmission destination candidates, wherein the information is related to an angle of arrival between each of the plurality of transmission destination candidates and an interference source, and the interference source corresponds to an interference signal; and selecting, by the circuitry, a transmission destination candidate from the plurality of transmission destination candidates based on the information, wherein the information indicates that the transmission destination candidate is one of most different in the angle of arrival of the interference signal from the interference source or not most similar in the angle of arrival of the interference signal from the interference source.
 16. A communication apparatus, comprising: a controller configured to control transmission, to an access point, of first information related to an intensity of each of a received plurality of an overlapping basic service set (OBSS) signals, wherein the first information includes basic service set (BSS) identification information, the BSS identification information indicates at least one of a first OBSS signal of a plurality of OBSS signals with first intensity or a second OBSS signal of the plurality of OBSS signals with second intensity, the first intensity of the first OBSS signal is maximum among intensities of the plurality of OBSS signals, and the second intensity of the second OBSS signal is minimum among the intensities of the plurality of OBSS signals.
 17. The communication apparatus according to claim 16, wherein the controller is further configured to control transmission, to the access point, of second information that associates the intensity of each of the received plurality of OBSS signals with basic service set (BSS) identification information of corresponding OBSS.
 18. A communication apparatus, comprising: a controller configured to control transmission, to an access point, of first information related to an intensity of each of a received plurality of an overlapping basic service set (OBSS) signals, wherein the first information includes basic service set (BSS) identification information, the BSS identification information indicated at least one of a first OBSS signal of a plurality of an OBSS signals with first intensity or a second OBSS signal of the plurality of an OBSS signals with second intensity, the first intensity of the first OBSS signal is maximum among intensities of the plurality of OBSS signals, and the second intensity of the second OBSS signal is minimum among the intensities of the plurality of OBSS signals. 